Non-contact rotary power transfer system

ABSTRACT

A power delivery system includes a rotary transformer having a primary winding and a secondary winding and configured to transfer power between stationary coupling elements on a stationary side and rotational coupling elements on a rotational side. The rotational coupling elements share a central axis with the stationary coupling elements, and are adapted to rotate with respect to the stationary coupling elements. The power delivery system includes an isolation transformer that drives the primary winding of the rotary transformer, and a plurality of power inverter stages whose outputs are adapted to be summed and coupled to the rotary transformer. A plurality of output power converters receive transmitted power from the rotary transformer. A plurality of control elements, disposed on the rotating side, are configured to close a feedback loop on desired and actual performance of the output power converters, and to control the power inverter stages.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/517,329, filed on Nov. 23, 2009 and entitled “Non-Contact RotaryPower Transfer System,” which is a national phase entry of PCTApplication No. PCT/US07/88117, filed on Dec. 19, 2007 and entitled“Non-Contact Rotary Power Transfer System” and claims the benefit ofU.S. Provisional Application No. 60/876,055, filed on Dec. 20, 2006 andentitled “Isolated Modular, Multichannel And Multiphase ContactlessRotary Power Transfer System.” The U.S. Patent Application, PCTApplication, and Provisional Application are incorporated herein byreference.

BACKGROUND

The next generation of medical computed tomography (CT) equipment mayhave to address increasing demands for operational modalities andreduced patient dose. Modalities such as real-time cardiac imaging mayrequire faster rotational speeds, and high voltage responses with higherpeak powers. Increased power may require more disc space for increasedtube cooling and more space for the traditional high voltage powersupply. It is desirable to provide solutions to these challenges that donot place excessive constraints on a CT design. The need for reliableperformance at higher rotational speed and power may require a newapproach to rotational high voltage power generation.

SUMMARY

A power delivery system may include a rotary transformer having aprimary winding and a secondary winding. The rotary transformer isconfigured to transfer power between one or more stationary couplingelements disposed on a stationary side of the rotary transformer, andone or more rotational coupling elements disposed on a rotating side ofthe rotary transformer. The rotational coupling elements share a centralaxis with the stationary coupling elements, and are adapted to rotatewith respect to the stationary coupling elements.

The power delivery system may further include an isolation transformeradapted to drive the primary winding of the rotary transformer, and aplurality of power inverter stages. The plurality of power inverterstages are configured to provide input power to the primary winding ofthe rotary transformer. The outputs of the power inverter stages areadapted to be summed and coupled to the isolation transformer.

The power delivery system may further include a plurality of outputpower converters that are configured to receive transmitted power fromthe rotary transformer, and to convert the received power to a desiredrange for the rotational coupling elements.

The power delivery system further includes a plurality of controlelements disposed on the rotating side of the rotary transformer. Theplurality of control elements are configured to close a feedback loop ondesired and actual performance of the plurality of output powerconverters, and to provide to the stationary side of the rotarytransformer one or more timing signals to control the power inverterstages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a non-contact power transfer system in accordancewith one embodiment of the present disclosure.

FIG. 2 shows a diagram of a connection of a non-isolated inverter to theprimary winding of the rotary transformer.

FIG. 3 provides a more detailed illustration of an isolation transformerthat operates between the inverter output and the primary of arotational power transformer.

FIG. 4 illustrates a distributed AC/AC module that includes a boostpre-regulator and that is coupled to a bridge inverter and an isolationtransformer.

FIG. 5 illustrates high power, lower frequency resonant currentwaveforms without phase shifting.

FIG. 6 illustrates phase shifting at higher frequency, which achieveslow power.

FIG. 7 illustrates non-contact control of delivered power with directgate drive and bi-directional supervisor communication.

FIG. 8 illustrates an electrostatic shield that shields the windings ofthe rotating transformer.

FIG. 9 illustrates a low force galvanic connection that prevents staticcharge build up on the rotating element due to friction with the air.

FIG. 10 illustrates a system level diagram of the non-contact powertransfer system illustrated in FIG. 1.

FIG. 11 is a system level diagram of a CT system that utilizes thenon-contact power transfer system illustrated in FIGS. 1 and 10.

DETAILED DESCRIPTION

Systems and methods are described that deliver power to a rotatingsystem without physical contacts (such as brushes) and at high speeds(for example greater than about 300 RPM), while increasing the availablespace on the rotating gantry by relocating the large power inverter ofthe high voltage and auxiliary power supplies to the stationary frame.In particular, a rotary transformer that couples power between astationary side and a rotating side is described. Isolation anddecoupling of the main power supply is achieved through an isolation andsumming transformer that drives the primary winding of the rotarytransformer in a multi phase configuration. Applications that may usethe non-contact power delivery system described in the presentdisclosure include, but are not limited to, CT (computed tomography)systems.

FIG. 1 illustrates a non-contact power transfer system 100 in accordancewith one embodiment of the present disclosure. While the embodimentillustrated in FIG. 1 may be used in CT scanners as illustrated in FIG.11, in different embodiments of the present disclosure the system 100may be used in applications other than CT, and in particular in anyapplication that requires transfer of induced power between one or morestationary elements and one or more rotational elements.

In particular, the system 100 illustrated in FIG. 1 includes: a split(or gapped) rotary transformer 110; a set 101 of modular power inverterstages 102; a balanced and shielded isolation/summing transformer 103;and an auxiliary transformer 146 whose output is regulated by anauxiliary output regulator 106. A gapped rotary transformer is alsocommonly referred to as a ring. In this patent, the terms “rotarytransformer” and “ring” have the same meaning, and are usedinterchangeably. In the embodiment illustrated in FIG. 1, the powerdelivery system 100 is configured to deliver power to an x-ray tube 185.In other embodiments, the power delivery system discussed in the presentdisclosure may be configured to deliver power to devices other than anx-ray tube.

The rotary transformer 110 transfers power between one or morestationary coupling elements located on a stationary side 170 of therotary transformer, and one or more rotational coupling elements locatedon a rotational side 171 of the rotary transformer 110. The rotationalcoupling elements are adapted to rotate with respect to the stationarycoupling elements, and share a common axis with the stationary couplingelements. The rotary transformer 110 has a primary winding(s) 131 and asecondary winding(s) 132, and transfers induced power to a high voltageoutput module(s) 125 connected to the secondary winding(s) 132.

The design shown in FIG. 1 utilizes a high frequency, high powerinverter system 120 that includes the above-mentioned set 101 of lowerpower inverters 102. Power is supplied through a mains input 127, whichis the power source from the electric power facility. The isolationtransformer 103 has a primary winding(s) 112 and a secondary winding(s)113. The outputs of the inverters 102 are adapted to be summed at theprimary winding 112 of the isolation and summation transformer 103. Thesecondary winding 113 of the isolation transformer 103 drives theprimary 131 of the gapped rotary transformer 110 that transfers inducedpower to the high voltage output module 125.

The set 101 of modular power inverters 102 are located on the stationaryside 170 of the rotary power transformer 110. The multiple AC/AC highfrequency inverter modules 102 may each include an integrated mainsinput rectifier, boost pre-regulator and full bridge inverter configuredin a non-series resonant topology. The pre-regulator may be configuredas a boost stage so as to provide wide compliance for nominal 380-480main power supplies that optimizes post inverter efficiency, asillustrated and described in more detail in conjunction with FIG. 4.

The balanced and shielded isolation/summing transformer 103 sums thefull bridge inverter outputs 112, and isolates the outputs 112 from theprimary winding 131 of the rotary transformer 110. The isolation andsumming transformer 103 provides double isolation from the main powersupplies 101 to the primary winding 131 of the rotary transformer 110.

In the illustrated embodiment, the isolation transformer 103 is a doubleinsulation (DI) element that acts as a balanced, shielded, highfrequency safety isolation transformer. The isolation transformer 103substantially reduces leakage currents that are normally induced intothe housing of the rotary transformer 110 via multiple capacitiveshields. The isolation transformer 103 also provides a center point thateliminates imbalanced common mode voltages driving the primary winding131 of the rotary transformer 110. Housed within the inverter, theisolation transformer 103 provides for a low noise, non-earth baseddrive signal to the primary winding 131 of the rotary transformer 110.The isolation transformer 103 also provides the full voltage isolationrequired by safety regulations without requiring the rotarytransformer's primary to secondary windings to provide anything morethan functional insulation. In this way, the need for a PE groundconnection capable of handling high fault currents to the rotationalcoupling elements is eliminated.

The main power source is derived from multiple inverters 102, eachoperating in a plurality of modes. In one embodiment, variable frequencymay be employed to maintain a wide range of power delivery in a resonantconfiguration by moving the operating frequency away from the resonantfrequency. Phase shifting at high frequencies substantially extends theoutput regulation, down to virtually 0% of output power. The selectivedisengagement of multiple inverters may also be employed for increasedefficiency at low power levels. The above-described approach allows forefficient power conversion and power regulation, by reducing theswitching losses at high power conditions and allowing for minimalcirculating currents in the resonant circuit for low power modes. Thetopology of the power transfer system 100 further provides completeoutput power control using a phase shift technique of the inverterbridge to the primary 112 of the isolation transformer 103. This phaseshift technique reduces high circulating current in the secondary of therotary transformer 110, which further improves efficiency.

In the illustrated embodiment, multiple inverters can be selected on thefly to add or subtract power delivery at the isolation and summingtransformer 103, to manage a dynamic load resulting from a fast timevarying emission current requirement imposed by new image and dosemanagement protocols while maximizing efficiencies. Variations in theoperating frequency of the inverter system relative to the resonantfrequency in the high voltage LC circuit provide an impedance mismatchaltering the power delivery. A dynamic range of about 1:20 may beachieved over a range of operating frequencies while phase shifting ofmultiphase inverters provides for an output substantially near 0%.

Auxiliary Power

Auxiliary power may be provided by inverters that are located on thestationary side 170 of the rotary transformer 110 and that operate at afixed frequency and duty cycle. In the embodiment illustrated in FIG. 1,auxiliary power is provided through an additional inverter 144 that isalso isolated, via an auxiliary isolation transformer 145, from anauxiliary winding 146 and separate multi output transformer 156, whichoperates continuously with load regulation from the auxiliary outputregulator 106 for multiple voltage outputs on the rotating side 171managed directly by a control element 105 located on the rotating side.

As shown in FIG. 1, a bi-directional low speed supervisory communicationpath is incorporated into a gate drive control winding 166 by modulatingthe data with a high frequency carrier. Regulation of the variousoutputs is performed on the rotating side 171, eliminating the feedbackrequirement to the stationary side 170 and providing for fast responseto load variations. A multi-tapped transformer winding 156 connected tothe secondary of the auxiliary winding 146 of the rotary transformer 110provides for various output voltages each with their own regulatingcircuit on the rotating side 171. This technique provides for isolationbetween the main auxiliary power supplied to the cooling system and tubedrive circuitry from that of the sensitive data collection circuits. Analternative construction of a multi tapped secondary ring windingprovides equivalent function at reduce space.

Feedback and Control

In the embodiment illustrated in FIG. 1, the feedback and control of themain stationary side inverters 102 are managed on the rotation side 171and only simple timing signals are provided to the stationary basedinverters 102 through a coupled control winding. In this way, theultra-high speed, non-contact digitized, transmission systems to controlthe stationary elements are eliminated. In particular, all control ofthe delivered power (not limited to high voltage) is performed via oneor more control elements 150 located on the rotating side. The highfidelity feedback required for fast rate of rise on the high voltageoutput is maintained by analog circuitry on the rotating side withoutdigitization, coding, and transmission thereby eliminating the need fora high bandwidth data link. As seen in FIG. 1, the control element(s)150 may receive input information from a CT system, in embodiments inwhich the power transfer system 100 is used for the CT system.

The one or more control elements 150, disposed on the rotating side ofthe rotary transformer, are configured to close a feedback loop ondesired and actual performance of the output power converters, andprovide to the stationary side of the rotary transformer one or moretiming signals to control the power inverter stages.

The control element 150 may comprise a control loop circuit configuredto close a feedback loop on desired and actual performance of outputpower converters that receive transmitted power from the rotarytransformer and convert the received power to a desired range for therotational coupling elements. The control loop circuit, which determinesthe required sub μsec timing of phase and pulse width of the inverters'gate drive control signals, is maintained and presented via timingsignals in an analog representation. These timing signals aretransmitted to the stationary side 170. As the timing signals areanalog, they maintain the real time information while requiring nofurther processing and can immediately be applied to the power invertergate drive circuitry 104 in the original form without latency or delay.

The windings of the rotary transformer are further adapted for dual usethat allows for bi-directional communication through superposition ofone or more coupled high-frequency modulated signals. The dual use mayinclude a first use in which power signals or timing signals aretransmitted through the windings, and a second use that provides forbi-directional communication. In the embodiment illustrated in FIG. 1,the bi-directional communication may be between the gate drive circuitry104 and a stationary supervisor circuit 175. The stationary supervisorcircuit 175, in turn, may be connected to a diagnostic/control interface180.

Isolation/Shielding

FIG. 2 shows a diagram of a connection of a conventional inverter 281 tothe primary winding of a rotary transformer 290, in a design in whichthe primary winding of the rotary transformer 290 is not isolated fromthe mains input. As shown in FIG. 2, the rotary transformer 290 includesa primary winding 291, a secondary winding 292, a primary housing 293for the primary winding 291, and a secondary housing 294 for thesecondary winding 292. In the diagram illustrated in FIG. 2, a mainsinput rectifier 285 feeds a high frequency inverter 281 that drives theprimary winding 291 in the rotary transformer housing 293, providing asource of current flow referenced to earth through parasiticcapacitances 286 (C1), 287 (C2), and 288 (C3) in the rotary transformer290. The capacitance between the primary winding 291 and housing 293(which is referenced to the grounded chassis frame) provides a path forthe current i, which is given by:

i=2·n·V·fC   (1)

In equation (1) above:

V=the applied voltage or in the case of a full bridge inverter the bussvoltage minus loss;

f=operating frequency of the inverter; and

C=the capacitance between the winding and the frame or housing.

The above-described coupling action to the secondary winding 192 alsoprovides a current source to charge the rotating structure and requiresa high current galvanic path to ground for a single fault condition onthe secondary side, defeating the value and concept of “non-contact”power transfer.

Referring to FIG. 3, a more detailed illustration is provided for theisolation transformer 303, which is shown as operating between theinverter output and a primary winding of a power rotary transformer 310.

As seen in FIG. 3, the rotary transformer 310 includes a primary winding311, a primary housing 313 for the primary winding 311, a secondarywinding 312, and a secondary housing 314 for the secondary winding 312.

As shown in FIG. 3, a primary shield 315 is provided between the mainpower input to the primary winding 311 of the rotary transformer 310.The shield 315 provides a return path for the primary parasiticcapacitance 301 to return to the main power input, through a mainsreturn path 313. A secondary shield 302 shown in FIG. 3 on the secondarywinding of the isolation transformer 303 to ground removes the 360 Hzcomponent present on the primary shield 315 from being coupled to thesecondary winding of the transformer 303 by returning it to theinverter's PE ground point.

The high frequency isolation transformer 303 effectively eliminates allleakage currents and provides for a safe condition in situations thatinclude but are not limited to: failure of the insulation between theprimary housing 313 and the primary winding 311; primary/secondarywindings 311/312 insulation failure; or human contact with the primaryhousing 313 and/or the secondary housing 314.

FIG. 4 illustrates a distributed AC/AC that is coupled to an isolationtransformer 403, unlike the non-isolated configuration shown in FIG. 2.The isolation transformer 403 has a primary winding 413 and a secondarywinding 414. Also shown are the primary winding 404 and secondarywinding 405 of the gapped rotary transformer.

FIG. 4 illustrates a shield connection that is to either one leg of therectified input of the main power supply, or to a center potential, asillustrated through reference numeral 406 in FIG. 4. When the shieldconnection is to such a low frequency point (e.g., about 360 Hz), theleakage current is provided a return path to reduce the transferredenergy (leakage) to and/or from the secondary winding 414 of theisolation transformer 403.

As shown in FIG. 4, the isolation transformer 403 allows for multiplewindings on the primary of the transformer, where the multiple windingscan connect to desired ones of a plurality of inverters. In this way,the collective outputs of the inverters can be summed to a singleoutput, rather than the inverters being galvanically connected directly.

An embodiment of the boost inverter stage is shown in FIG. 4. The booststage 401 consists of an input rectifier 400, boost inductor 407, boostswitch 409, and boost diode 408. The output voltage of the boost stageis controlled via PWM of the boost switch. Alternate configurations inwhich inductor location is relocated to the AC side of the mainsrectifier can be implemented.

Series resonant inverters that turn off the switching elements prior tocompletion of the resonant half cycle are operating above resonance andhence are referred to as “above resonant inverters”. The turn off of aswitch directs the current to be conducted through the anti-paralleldiode of a complimentary switch allowing it to turn on under zerovoltage. Turn off under current requires a fast switch/diode to reducethe turn off losses, a feature of FETs (Field-Effect Transistors). Athigher power levels, the on resistance of the FET results is significantand limits power handling capabilities. Recent improvements in IGBT(Insulated Gate Bipolar Transistor) technology has allowed IGBTs to beused successfully at lower voltages (<1200V) and currents (<100).However, IGBTs in large power devices (1200V@600 A) have limitedavailability of the type required for very high power (>100 kW) that canalso operate at switching frequencies over 50 kHz with low losses.

Above resonant inverters provide power regulation by moving away fromresonance to a higher frequency that provides changes to the resonantimpedance as defined by the Q of the circuit. Practical limitations instability and the speed of high voltage rectifiers significantly limitthe dynamic range of the output power for a series resonant system.

An alternative mode of operation for a series resonant circuit is belowresonance. In such a system the switches turn off after the half cyclecompletes while the resonant energy circulates through an anti-paralleldiode of the switch, allowing the device to turn off under zero current.Below resonant inverters have limitations at minimum power, because theyare difficult to operate in a discontinuous manner without introducingsignificant ripple in the regulated output.

In accordance with one embodiment of the present disclosure, a variablefrequency/phase inverter operates from near resonance to above resonanceutilizing the reflected capacitance in the load circuitry presented inparallel to the transformer inductances of the power circuit (non-seriesresonant). The advantage is a reduction in circulating currents at aboveresonant operation (lower power), offering a well behaved power stagethat can cease operation mid inverter cycle (for arc control), provide awide range of output power and eliminate the need for highcurrent/voltage capacitor elements in series with the main powertransmission.

FIG. 5 illustrates high power, lower frequency resonant currentwaveform(s) 500 without phase shifting of the inverter voltage source501. As illustrated in FIG. 5, maximum power is derived while atresonance, and continuously decreases as the frequency is increased.

To further extend the dynamic range of the power transfer systemdescribed in the present disclosure, phase control of the multi-phasewindings may be utilized, in one embodiment of the present disclosure.The high voltage secondary winding may exhibit a parasitic capacitance,in conjunction with that of the high voltage output stages reflected tothe primary side. They reduce, and may even eliminate, the need for acapacitive element to be added.

FIG. 6 illustrates resonant current waveforms 601 with phase shiftingpresent at the inverter drive voltage 602. As illustrated in FIG. 6, thecurrents are reduced. At approximately 2.5 times the resonant frequencythe phasing of the multiphase inverters at the primary of the isolationtransformer are altered, thereby further reducing the transferred power.In this manner zero output power can be achieved while limiting theupper operating frequency. Additionally, the phase shifted waveforms arepreferably canceled and/or combined at the inverter stage or the primaryside of the isolation transformer, as opposed to being canceled in theprimary of the HV transformer, thereby preventing the creation of largecirculating currents in the transformer windings. These circulatingcurrents create heat, reduce efficiency, and limit duty cycle of thepower transfer system.

FIG. 7 illustrates non-contact control of delivered power with directgate drive and bi-directional supervisor communication. As in previousfigures, FIG. 7 illustrates a rotary transformer 710 that is configuredto transfer induced power between a stationary side 730 and a rotatingside 740. In the embodiment illustrated in FIG. 7, the critical realtime gate drive signal timing is generated by a control loop circuit709, and is presented to drive circuits 703, 708 which utilize rotarytransformer windings 720 (T_(A)), (T_(B)) as part of the gate drivetransformers. They have a 1:1 ratio in the illustrated embodiment.Different ratios may be used in different embodiments. In this techniquethe timing of both gating signals is preserved in the analog signal forpulse width and relative phase. While two timing channels, 720(T_(A)),(T_(B)), are shown in FIG. 7, the number of timing channels isnot limited to two, and any other number of timing channels may beincluded in other embodiments of the present disclosure.

In the illustrated embodiment, a bi-directional communication channelbetween the stationary and rotating elements is accomplished by superpositioning a very high frequency signal on the timing waveforms of 720.Data is sent to the rotating side 740 by using modulator 701 andextracting the data via a demodulator 704. The very high frequencysignal riding on the gate drive signal is removed via a filter 702 andpresented directly to the gate drive circuitry of a plurality ofinverter modules 705. This process is likewise used to send data to thestationary side 730 using modulator 707 and demodulator 706.

The demodulated signal is then processed to provide non-real timecontrol functions, including but not limited to diagnostics, status andinterlocks features.

In the illustrated embodiment, the real-time gate drive control signalsand non real-time data are sent via coupled windings contained withinthe rotary transformer elements 720 (T_(A), T_(B)). It should beappreciated that control of the power delivery system is not limited tothe above-described technique, and that transfer mechanisms may be usedfor the same purpose, in different embodiments of the presentdisclosure.

FIG. 8 illustrates an electrostatic shield 800 that shields the windings801 of the rotary transformer. The e-field of the primary and secondarywindings of a transformer produce radiated emissions. The nature of arotary transformer requires a gap that prevents the winding from beingshielded by the housing. As seen in the embodiment illustrated in FIG.8, a non-overlapping foil shield 800 is provided on an exposed surfaceof the winding 801. The shield is made of, and/or includes, a conductingfoil and an insulating material 803. Examples of the insulating material803 include, but are not limited to, a 2 millimeter layer of Kapton toprevent a “shorted turn”. The foil is comprised of an appropriatematerial to minimize eddy currents. Different types of insulatingmaterial 803 may be included in different embodiments of the presentdisclosure. A high permeability magnetic core 806 may surround thewinding 801. One side of the shield 800 is connected to the rotarytransformer (or ring) frame 802 or to an alternative return path, whenusing the above-described isolation method, further reducing radiatednoise.

Electrostatic Discharge

The various aspects of the power transfer system design described inthis disclosure provide for an effective solution to high speed, nomaintenance rotary power transfer. Although a non-contact arrangementfor power transfer is a desirable feature to eliminate brush wear fromexisting designs, a need for a low force, non-power, non-signal relatedgalvanic connection may arise. Without a galvanic path (such as an airbearing configuration) there can be a static charge build up on therotating element due to friction with the air.

FIG. 9 illustrates a low force galvanic connection, or other type ofelectrostatic discharger, that prevents static charge build up on therotating coupling element due to friction with the air. In FIG. 9, astationary ring frame 902 and a rotating ring frame 903 are shown, wherethe rotating ring frame 903 is rotatable about the stationary ring frame902 around an axis of rotation 910. A simple low force connection, suchas a connection 901 shown in FIG. 9, provides such a galvanic path, orother type of electrostatic discharger. The orientation of the drainelement(s) is such that the centripetal force 911, due to the rotationabout the axis 910, provides the required contact force. An additionalfeature of the design is to increase bearing life in a CT system of thetype using traditional bearing, by eliminating micro-discharges throughthe bearing and race which can otherwise reduce the life time of thebearing.

It should be appreciated that discharge path or “drain wire” of thepower delivery system is not limited to a galvanic connection or theabove-described technique, and that different transfer mechanisms may beused for the same purpose, in different embodiments of the presentdisclosure. As just one example, in one embodiment the electrostaticdischarger may be an ionic connection, rather than a galvanicconnection. In this embodiment, an ionic source may be employed in orderto neutralize charge build up.

FIG. 10 illustrates a system level diagram of a non-contact powertransfer system 1000, also shown in FIG. 1. The non-contact powertransfer system 1000 includes a plurality of modular inverters 1010 withpre-regulators of the type described in conjunction with FIG. 4. Theoutputs of these modular inverters 1010 (three shown as an example) aresummed by multiple shielded isolation transformers 1020 of the typeshown and described in conjunction with FIG. 1. These isolationtransformers 1020 are configured to drive a rotary transformer 1030.

A regulator 1040 isolates and regulates various auxiliary outputs. Thesecondary windings of the rotary transformer 1030 associated with themain inverter module 1010 are connected to high voltage module(s) 1070.The non-contact power transfer system 1000 includes the electrostaticshield and discharge element described above, with integrated real timegate drive and bi-directional communication.

In the illustrated embodiment, the non-contact power transfer system1000 is configured to deliver power to an x-ray tube 1005. A kV, mA, andfilament control communication link 1060 is shown. In the illustratedembodiment, in which the power transfer system 1000 is shown as beingused for a CT system, the control communication link 1060 communicateswith CT control unit(s) in a CT system, for example receiving CT controlinformation and generating status information. The link 1060 alsocommunicates with the high voltage modules 1070, and is connected to thesecondary windings of the rotary transformer 1030. An inverter controlcommunication unit 1050 is also shown. This unit receives diagnosticstatus and control information, and communicates the receivedinformation to the inverters 1010.

FIG. 11 illustrates a system level diagram of a CT system 1100 thatutilizes the non-contact power delivery system 100 illustrated inFIG. 1. As explained in conjunction with FIGS. 1 and 10, the powerdelivery system 100 transfers power between a stationary side 1170 and arotational side 1171. An isolation transformer 1140 is located on thestationary side 1170.

In a conventional CT system, a source of x-rays (typically an x-raytube) and x-ray detector array(s) are typically mounted on a rotatinggantry. In the CT system 1100 illustrated in FIG. 11, an x-ray tube 1105and a data acquisition system 1110 are disposed on the rotational side1171. The data acquisition system 1110 acquires and processes x-raydata, which are generated when the x-rays from the x-ray tube 1105 aredetected by x-ray detector array(s) in the data acquisition system,after the x-rays have traversed through a target object. The x-ray dataare transmitted by a transmitter 1120 to a CT image reconstruction unit1130 disposed on the stationary side 1170, via a receiver 1125. The CTimage reconstruction unit 1130 uses image processing and reconstructionalgorithms, which may include but are not limited to interpolation andbackprojection, to reconstruct a tomographic image of the target objectusing the x-ray data transmitted from the rotational side 1171 to thestationary side.

The CT system 1100 illustrated in FIG. 11 represents only one example ofsystems in which the non-contact power delivery system described abovecan be used. The non-contact power delivery system may be used in anyapplication that requires transfer of power between a stationary sideand a rotational side. A number of features disclosed in the presentdisclosure may be useful in power delivery systems, and are summarizedbelow.

A device is described that isolates one or more outputs of a powerinverter system from a primary winding of a rotary transformer. Therotary transformer adapted to couple power between at least onestationary element and at least one rotational element. The powerinverter system is configured to provide input power to the primarywinding of the rotary transformer. The device includes an isolationtransformer configured to receive a sum of the one or more outputs ofthe power inverter system and to drive the primary winding of the rotarytransformer.

A control system is described that controlling delivery of power by arotary transformer that has a primary winding and a secondary windingand that is configured to transfer power between stationary couplingelements disposed on a stationary side and rotational coupling elementsdisposed on a rotating side. The control system includes one or morecontrol elements disposed on the rotating side. The control elements areconfigured to provide timing signals to the stationary side in order tocontrol one or more power inverter stages that provide input power tothe primary winding of the rotary transformer.

The control elements including at least one control loop circuit that isdisposed on the rotating side and that is configured to control deliveryof power from the secondary winding of the rotary transformer. Thecontrol loop circuit is configured to close a feedback loop on desiredand actual performance of one or more output power converters. Theoutput power converters receive transmitted power from the rotarytransformer, and convert the received power to a desired range for therotational coupling elements.

The control system may further include gate drive windings that arecoupled to the control loop circuit, and are configured to transmit realtime gate drive waveforms from at least some of the rotational couplingelements to at least some of the power inverter stages.

An electrostatic discharger is described for a non-contact powerdelivery system that transfers power between one or more stationarycoupling elements, and one or more rotational coupling elementsconfigured to rotate with respect to the stationary coupling elements.The electrostatic discharger is configured to substantially preventstatic discharge from accumulating on one or more of the rotationalcoupling elements.

In one embodiment, the electrostatic discharger may be a galvanicconnection between the rotational coupling elements and the stationarycoupling elements.

A rotary transformer is described that is used in a power deliverysystem. The rotary transformer transfers power between stationarycoupling elements on a stationary side of the transformer and rotationalcoupling elements on a rotational side of the transformer. The rotarytransformer includes a primary winding and a secondary winding. Thewindings of the rotary transformer are configured for dual use thatallows for bi-directional communication through one or more coupledhigh-frequency modulated signals. Such a dual use may comprise a firstuse in which power signals or timing signals are transmitted through thewindings, and a second use that provides for bi-directionalcommunication between the stationary side and the rotational side.

In summary, an isolated multichannel, contactless, modular rotary powertransfer system has been disclosed that includes a split rotarytransformer that couples one or more stationary elements with one ormore rotational elements. An isolation and summing transformer drivesthe primary of the rotary transformer in a multi phase configuration,and sums the stationary power elements in a dynamic manner to respond toload conditions. The secondary winding of the rotary transformer drivesselected rotational elements to produce a desired range of regulatedpower. The rotational based control that provides variable frequency andphase control of the power stages and multiple windings of therotational element(s) eliminate high bandwidth digitized data transferto the stationary side, providing a wide dynamic range of output power,high efficiency, and fast rise times.

While certain embodiments have been described of a power transfersystem, it is to be understood that the concepts implicit in theseembodiments may be used in other embodiments as well. The protection ofthis application is limited solely to the claims that now follow.

In these claims, reference to an element in the singular is not intendedto mean “one and only one” unless specifically so stated, but rather“one or more.” All structural and functional equivalents to the elementsof the various embodiments described throughout this disclosure that areknown or later come to be known to those of ordinary skill in the artare expressly incorporated herein by reference, and are intended to beencompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public, regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed under the provisions of 35 U.S.C. §112, sixth paragraph,unless the element is expressly recited using the phrase “means for” or,in the case of a method claim, the element is recited using the phrase“step for.”

What is claimed is:
 1. A control system for controlling a power inverterdisposed on a stationary side and configured to deliver power to a firstelement disposed on a rotating side, the control system comprising: acontrol element disposed on the rotating side and configured to generatea timing signal for controlling the power inverter; and a rotarytransformer configured to transmit the timing signal from the rotatingside to the stationary side and comprising: a first gate drive windingdisposed on the rotating side and coupled to the control element; and asecond gate drive winding disposed on the stationary side and coupled tothe power inverter.
 2. The control system of claim 1, the controlelement configured compare a desired operating parameter of the firstelement to an actual operating parameter of the first element and tomodify the timing signal based upon a difference between the desiredoperating parameter and the actual operating parameter.
 3. The controlsystem of claim 2, at least one of: the desired operating parametercorresponding to a desired voltage to be applied to the first elementand the actual operating parameter corresponding to an actual voltageapplied to the first element; or the desired operating parametercorresponding to a desired current to be supplied to the first elementand the actual operating parameter corresponding to an actual currentsupplied to the first element.
 4. The control system of claim 1, thefirst element comprising a radiation source.
 5. The control system ofclaim 1, comprising gate drive circuitry disposed on the stationary sideand configured to send, via the rotary transformer, a firstcommunication signal to the control element.
 6. The control system ofclaim 5, the first communication signal describing a desired operatingparameter of the first element.
 7. The control system of claim 5, thecontrol element configured compare the desired operating parameter to anactual operating parameter of the first element and to modify the timingsignal based upon a difference between the desired operating parameterand the actual operating parameter.
 8. The control system of claim 1,the control element configured to send, via the rotary transformer, afirst communication signal to a second element disposed on thestationary side.
 9. The control system of claim 8, the firstcommunication signal describing an operating status of the firstelement.
 10. The control system of claim 1, comprising gate drivecircuitry disposed on the stationary side and wherein: the gate drivecircuitry is configured to send, via the rotary transformer, a firstcommunication signal to the control element; and the control element isconfigured to send, via the rotary transformer, a second communicationsignal to the gate drive circuitry.
 11. The control system of claim 1,the control element configured to generate a first communication signalfor transmission, via the rotary transformer, to a second elementdisposed on the stationary side, the first communication signal ridingon the timing signal.
 12. The control system of claim 11, comprisinggate drive circuitry disposed on the stationary side and configured tofilter the first communication signal from the timing signal.
 13. Thecontrol system of claim 1, the timing signal remaining in an analogdomain between the control element and the power inverter.
 14. Thecontrol system of claim 1, the control element configured to generate asecond timing signal for controlling a second power inverter disposed onthe stationary side and the rotary transformer comprising: a third gatedrive winding disposed on the rotating side and coupled to the controlelement; and a fourth gate drive winding disposed on the stationary sideand coupled to the second power inverter, and wherein: the first gatedrive winding and second gate drive winding operate in tandem to deliverthe timing signal between the control element and the power inverter;and the third gate drive winding and fourth gate drive winding operatein tandem to deliver the second timing signal between the controlelement and the second power inverter.
 15. The control system of claim14, comprising gate drive circuitry disposed on the stationary side andwherein: the gate drive circuitry is configured to send, via the firstgate drive winding and the second gate drive winding, a firstcommunication signal to the control element; and the control element isconfigured to send, via the third gate winding and the fourth gatewinding, a second communication signal to the gate drive circuitry. 16.The control system of claim 14, the power inverter comprising a highvoltage power inverter for generating first power to be supplied to ahigh voltage load and the second power inverter comprising an auxiliarypower inverter for generating second power to be supplied to a lowervoltage load.
 17. A computed tomography (CT) system, comprising: aradiation source disposed on a rotating side of the CT system; adetector array disposed on the rotating side of the CT system; a powerinverter disposed on a stationary side of the CT system and configuredto inverter power generated by a power source; and a control elementdisposed on the rotating side and configured to generate a timing signalfor controlling the power inverter.
 18. The CT system of claim 17,comprising: a rotary transformer configured to transmit the timingsignal from the rotating side to the stationary side and comprising: afirst gate drive winding disposed on the rotating side and coupled tothe control element; and a second gate drive winding disposed on thestationary side and coupled to the power inverter.
 19. The CT system ofclaim 18, the rotary transformer configured to transmit a communicationsignal between the control element and a second element disposed on thestationary side.
 20. A control system for controlling a power inverterdisposed on a stationary side and configured to deliver power to a firstelement disposed on a rotating side, the control system comprising: acontrol element disposed on the rotating side and configured to generatea timing signal for controlling the power inverter based upon acomparison between a desired operating parameter of the first element toan actual operating parameter of the first element, the timing signalremaining in an analog domain between the control element and the powerinverter.